The overall aim of this project is to clarify the relationship between neuronal activity in the internal segment of the globus pallidus (GPi) and the development, phenotypic distribution and severity of dystonic movements in patients with primary generalized (PGD) and cervical dystonia (CD). Three fundamental questions will be addressed: 1) What are the physiological characteristics of neurons in the basal ganglia in patients with PGD and CD? 2) Is there a relationship between those physiological characteristics ( e.g. mean discharge rate, somatosensory response properties, or the number of cells with bursting or power at low oscillatory frequencies) and clinical measures of dystonia severity (Burke Fahn Marsden Dystonia Rating Scale for PGD and Toronto Western Spasmodic Torticollis Rating Scale for CD)? and 3) Is there a difference in the relative proportion and distribution of neurons in the GPi that demonstrate these dystonic characteristics between patients with PGD and those with CD? Neural and force control data will be gathered simultaneously in the operating room during microelectrode mapping of the GPi as part of deep brain stimulation surgery. As part of this two-year project, neuronal, EMG and force control data will be collected from 18 (9 PGD and 9 CD) dystonia patients. Specific Aims 1 and 2 are focused on determining the relationship between neuronal activity (i.e. mean discharge rate, pattern, oscillatory activity and somatosensory response properties) within the GPi and the severity of PGD and CD, respectively. The final phase of Aims 1 and 2 will be to compare the neural activity within the GPi in patients with PGD and CD. This comparison will allow us to determine if PGD and CD patients have common alterations in neural activity or if each type of dystonia has its own unique'pathophysiology. In Specific Aim 3, patients will perform a force-tracking motor task during the recording of neural activity within GPi. Motor performance will be objectively quantified using biomechanical measures. The simultaneous collection of neural and motor data is unique and will clarify the relationship between neuronal activity within the GPi of PGD and CD patients and their specific impairments in the control of muscle forces, in particular the scaling and focusing of force. Identifying specific physiological characteristics associated with dystonia, determining the spatial segregation of affected neurons in PGD and CD and understanding the specific motor impairments of each will refine current surgical strategies and may lead to new surgical approaches to relieve dystonic symptoms.